1. Field of the Invention
This invention relates to a mechanism which will sense the lateral forces which act upon a trailer tongue coupler. The present invention is a type of surge-bake control for applying the brakes of a towed vehicle, such as a trailer, independent of the application of the brakes of the towing vehicle. The present invention teaches a mechanism which will respond to lateral, or sideways, accelerations of the trailer, to momentarily apply the trailer's brakes to preclude further instabilities, such as are known to affect straight line motion of certain trailed vehicles.
Trailer towing involves the mating of a towing vehicle to the towed vehicle, such that there is essentially an articulated vehicle combination. For safety, large trailers require separate braking systems, to assist in the slowing down of the total articulated combination. As is known, most trailer brake systems either involve separate connections with the towing vehicle, or are of the surge-type, which operate independently of, but are synchronized with, the braking of the towing vehicle.
The present invention responds only to lateral forces and is of the surge type in that it comprises a selectively actuated brake actuator which requires no mechanical or other type of interconnection with the towing vehicle or the braking system of the towing vehicle. The lateral force limiting coupler assembly taught herein is a mechanism which will sense and respond to sideways or lateral forces which may be dynamically generated during the towing of a trailer. Dynamic instabilities may become a serious hazard. A lateral acceleration gain of a trailer, wherein it yaws to the left and the right of the center line of travel, may produce sudden instabilities of the articulated combination of the towing vehicle and the trailer, with resultant loss of control of the combination by the driver.
It is significant that the occurrence of lateral accelerations is an insidious phenomena. Severe yawing oscillations, once started, tend to reinforce themselves rather suddenly. The driver of a towing vehicle is oftentimes unaware at the outset of the first lateral accelerations and, therefore, is not able to apply corrective action well before external conditions may aggravate the problem.
It is known, for example, that an inexperienced driver may seriously aggravate the problem by applying the car brakes when a towed vehicle actually has begun to fishtail. However, an experienced towing vehicle operator will either accelerate to dampen out the lateral swing phenomena or selectively apply only the brakes on the towed vehicle, to apply a corrective reaction to the yawing motion. It should be remembered, that in articulated combinations having direct connection between the brakes of the towed vehicle and the brakes of the towing vehicle, an independent control for the towed vehicles brakes is available in the driver's compartment. Therefore, with such a separate control for the trailer's brakes available to the driver, he may selectively be able to apply only the trailer brakes to dampen out the onset of any oscillatory motion. However, even this form of correction necessarily requires that there be a trailer brake control within the driver's reach, as well as quick thinking on the part of the driver to selectively apply only the trailer's brakes.
A much different situation is presented when there is no such mechanical, electrical or hydraulic interconnection between the brake systems of the towed vehicle and the towing vehicle. For example, in the rental of utility trailers, there is no practical way of installing a separate override for the trailer brake system within the reach of the driver of the towing vehicle. As has been discussed, surge-brakes are normally self-contained within the trailer, and will rely upon the inertia of the trailer to actuate the brakes of the towed vehicle independently, though in synchronism, with the deceleration of the towing vehicle. Yet, surge-brake devices are responsive only to a linear deceleration of the trailer. They are not selectively responsive to lateral forces, such as are developed before a towed vehicle becomes noticeably unstable. Therefore, there has existed a great need for a completely self-contained device on towed vehicles which will respond to lateral forces, without requiring any type of mechanical, electrical or hydraulic interconnection with the towing vehicle.
2. Description of the Prior Art
The prior art is replete with teachings on the application of brakes on a towed vehicle, both independently of the application of the towing vehicle's brakes, and in direct connection with the braking function in the towing vehicle. The approaches of the prior art to the energization of brakes on a towed vehicle can be more fully appreciated with reference to the following U.S. Pat. Nos.: EWALD, 3,880,263; RENDESSY, 3,871,686; BULLINGER, 3,834,767; GAVIT, 3,833,928; SPARR, 3,810,521; ROSSIGNO, 3,790,807; HERBERT, 3,722,919; JUBENVILLE, 3,715,003; DOMBECK, 3,647,032; FRANZEL, 3,566,987; BUTLER, 3,527,324; GEARHART, 3,394,949; RENDESSY, 3,311,390; FRANZEL, 3,288,240; HAHN, 3,144,101; HART, 3,141,529; STAIR, 3,058,548; HENRY, 2,993,568; YADRO, 2,786,554; FIKSE, 2,630,888.
In summary, none of these patents teach a lateral force limiting coupler assembly characterized by having a pivotable coupler on the trailer tongue yoke for momentarily resisting dynamic lateral forces. While various of these patents allege an anti-sway function through application of the trailer brakes, none of them teach a completely self-contained lateral force correction device without interconnections to the trailer ball or the towing vehicle's electrical or hydraulic systems.
The surge-brake actuator construction of Ewald teaches a construction represented as an improvement over the construction of the Dombeck patent. Neither of these surge-brake assemblies are responsive to lateral forces, and merely represent improved versions of conventionally known surge-brake controls.
The patent to Rendessy illustrates a type of mechanical directional control which relies upon frictional restraint between a flexible line connected to the vehicle's bumpers and a roller assembly on the front yoke. As such, this flexible tensioning member applies corrective moments upon the vehicle's bumper for directional correction, and not upon the automatic and intermittent application of a trailer brake assembly, as taught herein.
The patent to Bullinger illustrates a self-contained wheel driven hydraulic pump brake assembly for a trailer, also responsive only to a longitudinally slidable connection between the tractor and the trailer.
The patent to Gavit illustrates another type of direction control which requires the mounting of an electro-mechanical sensor directly on the hitch of the towing vehicle. As such, the device of Gavit requires permanent installation on the hitch of the towing vehicle, and does not amount to a self-contained lateral force limiting device on the yoke on the trailer.
Similarly, the anti-fishtail device of Sparr requires a suitable electrical interconnection between the hitch ball and a sensor assembly mounted thereupon. Additionally, the electro-mechanical device of Sparr requires a power supply, and the accessory mounting of an appropriate switch assembly on the hitch itself.
The patent to Rossigno also teaches an electrical braking system which needs to be interconnected with the towed vehicle, and in no way contemplates a self-contained device for responding to lateral accelerations.
The anti-jackknife device of Herbert represents merely another prior art device which is neither functionally or structurally related to the force limiting coupler assembly disclosed herein.
The patent of Jubenville illustrates a rear mounted trailer accelerometer which senses only actual fishtailing through a ferro magnetic ball which travels past electro-mechanical contacts. As such, Jubenville's system also requires an external power supply and calibration of the travel of the ferro magnetic balls within a rear mounted accessory sensing device.
The patent to Franzel illustrates another electrical acceleration detector for energizing both brakes of a fishtailing trailer. For this purpose, Franzel employs mercury switches, mounted on either side of the towed vehicle, together with a power supply, with coordination of all switches necessary to obtain proper operation. Again, Franzel's device requires an electrical connection with the towed vehicle, so that adjustment and corrective brake action can be initiated directly by the driver.
The patent to Butler is of common assignment with the present application, and represents various known elements comprising a trailer coupling surge brake mechanism. Of course, Butler's device exemplifies surge brake systems without the additional capability of lateral force actuation.
The patent to Gearhart illustrates another form of mechanical anti-sway control requiring a series of lines, connected through separate attachment to the towing vehicle's bumpers, in order to correct a fishtailing situation. Again, this patent, like the other cited patents requiring separate connection to the towing vehicle, illustrate, by contrast, the advantages of a lateral force limiting coupler assembly which is completely self-contained and adaptable to all towing vehicles without any modification whatsoever. The patent to Rendessy illustrates an early manner of hitch design for applying a corrective moment directly from the towing vehicle's rear bumper.
The earlier patent to Franzel is pertinent for his teaching of an automatic stability control means for selectively applying either the left or right brakes on the towed vehicle. Again, however, the electrical circuitry according to Franzel requires a series of electrical switches and separate electrical power supply together with an interconnection with the towing vehicle. By contrast, the present invention obtains a significant operational simplicity over those exemplary devices which respond only to fishtailing, and require separate interconnections between the trailer and the towing vehicle.
Significantly, the patents to Hart, Hahn, Henry, Yadro and Fikse exemplify various other forms of surge-brake assemblies which are disclosed to be capable of responding only to longitudinal inertial forces. As such, these patents further represent the state of the art for surge-brake assemblies; without the capability of applying a selective braking control on the trailer brakes in response to lateral accelerations of a trailer.
Finally, the patent to Starr represents another well-known form of electro-hydraulic brake actuation by a separate connection, between towing vehicle and the towed vehicle. Again, by contrast, the advantages inhering in avoiding such interconnections between the trailer and the towing vehicle, as disclosed herein, may be further appreciated.